Zinc oxide particles, which have been used as a sunscreen ultraviolet blocking agent in cosmetic product applications, are ultrafine particles having an average particle diameter of 0.1 μm or less. For example, Patent Documents 1 and 2 disclose zinc oxide fine particles which can be used for ultraviolet blocking agents. These zinc oxide particles are also expected to be modified to have further excellent physical properties.
For example, the zinc oxide fine particles described in Patent Documents 1 and 2 have the problem that particles tend to be aggregated because they are fine particles, so that independency of particles are reduced, leading to an increase in oil absorption. An increase in oil absorption causes the disadvantage that when the particles are compounded in a cosmetic, oil components contained in the cosmetic are absorbed in a large amount, so that the viscosity of the cosmetic is increased. Further, there is also the disadvantage that particles are aggregated, so that dispersibility is deteriorated to reduce transparency, and therefore when a cosmetic containing these particles is used (applied to the skin), it appears unnaturally white. Further, it is also desired to enhance ultraviolet blocking performance and reduce the oil absorption and the volume of a powder.
Patent Document 3 discloses a production method in which a mixed liquid of a zinc compound, acetic acid and glycol is held at a temperature of 50 to 200° C. for 0.5 to 5 hours to generate zinc oxide fine particles having an average particle diameter of 200 nm or less. However, this production method is a method of obtaining a precipitate by heating a solution in which zinc oxide is fully dissolved, and zinc oxide particles obtained by this method are not preferable because particles having an aspect ratio of less than 2.5 cannot be obtained. Further, the production method is not suitable from an industrial point of view because expensive glycol is used.